In conventional planographic printing, a printing plate bearing as oleophilic, ink receptive, image is first dampened with an aqueous fountain solution to prevent the ink from wetting the hydrophilic, non-image bearing, area of the printing plate. Afterwards, an oil-based ink is rolled over the pate to selectively coat the now printable image. Conventional planographic printing has a number of problems inherent to having both an oleophilic ink and an aqueous fountain solution conjoined on the same press. First, the fountain solution applied to the printing plate flows back into the train of inking rollers on the press, causing emulsification of the ink. Second, it is difficult to maintain control of the delicate balance needed between the amount of ink and the amount to fountain solution one needs to apply to the printing plate. Consequently, image fidelity and uniformity is difficult to maintain. Third, the fountain solution tends to flow forward over the offset cylinder, moistening the copy paper and causing it dimensional changes. Finally, in those cases where the printing is imaged directly by electrophotography, the plate must be subjected to an etching treatment which makes the printing operation more complicated.
Considerable effort has been applied in the industry toward the development of printing plates that overcome some of the foregoing problems. A significant portion of that effort has been directed toward the development of planographic plates that do not require a fountain solution circulating in the printing apparatus to accomplish the printing function. These printing plates are referred to herein as "waterless" plates to distinguish them from conventional printing plates that employ aqueous fountain solution during printing operations. With waterless plates, the use of fountain solution is avoided by employing printing methods and plate compositions that do not rely on inducing hydrophilicity to a portion of the plate in order to distinguish the oleophilic image surface from the non-oleophilic non-image surface.
U.S. Pat. No. 4,342,820 teaches a negative working waterless plate that does not require dampening (i.e. fountain solution) for use in printing. The plate comprises a base substrate; a light releasing photosensitive layer, overlaying the base substrate; and a silicone rubber layer, overlaying the photosensitive layer. When the printing plate is exposed through a negative film and treated with a developer, only the silicone rubber layer overlaying the exposed photosensitive layer is removed, while the photosensitive layer remains as is to form the image area.
U.S. Pat. No. 3,894,873 teaches a positive working waterless plate comprising a base substrate; a light sensitive photoadhesive layer, overlaying a base substrate; and a silicone rubber layer, overlaying the photoadhesive layer. When the printing plate is exposed through a positive transparency and treated with a developer, only the silicone rubber layer overlaying the unexposed photoadhesive layer is removed, while the photoadhesive layer remains as is to form the image area.
Lithography and offset printing methods have long been combined in a compatible marriage of great convenience for the printing industry for economical, high speed, high quality image duplication in small runs and large. Known art available to the industry for image transfer to a lithographic plate is voluminous but dominated by the photographic process wherein a hydrophilic plate is treated with a photosensitive coating, exposed via a film image and developed to produce a printable, oleophilic image on the plate.
While preparing lithographic plates by photographic image transfer is relatively efficient and efficacious, it is a multi-step, indirect process of constrained flexibility. Typically, a photographically presensitized (PS) plate is prepared from a hydrophilically surface treated aluminum. A positive or negative film image of an original hard copy is prepared and the pre-sensitized plate exposed to the film image, developed, washed and made ready for print operations. Any desired changes in the film image must be made by first changing the original hard copy and repeating the photographic process; hence, the constrained flexibility. As sophisticated and useful as it is to prepare plates by photographic image transfer, the need for a lithographic plate fabricating process that obviates the above problems associated with the photographic process has long been recognized. Clearly, it would be highly beneficial to the printing industry to directly produce a quality printable image on a plate without proceeding through a multi-step photographic process. It would also be highly efficacious if a process were developed whereby changes could be made in an original image in some predetermined manner without incurring the need to correct hard copy and repeat the photography, particularly if those changes could be made "on line".
Progress in digital technology now enables printers to use direct to plate digital plate makers. The high speed of text printing provides considerable productivity improvements over the conventional analog mode of plate preparation. Digitally controlled devices alter the ink-receptivity of the plate in a pattern representative of the image to be printed. Such imaging devices include sources of electromagnetic radiation pulses produced by one or more lasers, or ink-jet sources that directly deposit ink repellent/accepting materials on the plate.
Image forming by digital computer aided design of graphical material or text is well known. Electronically derived images of words or graphics presented on the cathode ray tube (CRT) of a digital computer system can be edited and converted to final hard copy by direct printing with impact printers, laser printers or ink jet printers. This manner of printing or producing hard copy is extremely flexible and useful when print runs of no more than a few thousand are required but the print process is not feasible for large runs measured in the tens or hundreds of thousands of pieces. For large runs, printing by lithographic plate is still the preferred process with such plates prepared by the process of photographic image transfer.
It is known that digitized image information can be used in plate making wherein a film is made to express the image according to the image information digitization. An image is formed on the plate by exposure and development. While this method augments flexibility by permitting editing of a digitized image, the method does not overcome the problems associated with the photographic image transfer method of plate fabrication.
Recently, fabrication of lithographic or offset plates by ink jet technique has been proposed. One such technique is disclosed in Japanese Patent Kokai ShO62-25081 which describes the use of an ink jet system to apply an oleophilic liquid to form an image on the surface of a hydrophilic aluminum lithographic plate.
U.S. Pat. No. 4,833,486 discloses the use of an ink jet head to deposit a hot wax upon the surface of a lithographic plate. The hot wax solidifies upon contact with the plate, thus providing an instantaneous printing pattern. Plates prepared by this method are useful for very limited print runs of a few thousand pieces.
There are several advantages for fabricating printing plates by ink jet printers. One advantage is that such processes are environmentally friendly. The complex and potentially polluting chemical preparations and solvents ordinarily used in masking and stripping away photoresist areas of the plates are not always required with ink jet techniques.
Ink jet technology, however, is in its infancy with respect to commercial lithography. Present ink jet techniques cannot produce large or commercially acceptable offset plates. That is, the plates produced by present ink jet techniques have very low plate runs by commercial lithographic standards. Furthermore, there is no ink jet apparatus or process presently available for fabricating large offset plates having a plurality of pages disposed thereon. Indeed, U.S. Pat. No. 4,833,486 (described above) teaches that ink jet materials are inexpensive, and therefore, the printing plate may be used a minimum number of times and then discarded. Moreover, in one embodiment of this patent, it is indicated that the system is designed for non-commercial plate production, inasmuch as an office processor system is proposed.
Office processing systems ordinarily are not capable of providing the large amounts of digital information required to produce large, commercial lithographic plates.
A further drawback of the apparatus disclosed in the '486 patent is that it makes use of an ink jet medium which may be a wax. Wax is a soft material and will abrade with use under the conditions present for commercial offset printing. Even the so-called hard waxes will not provide the durability required for commercial printing runs of the order of 100,000 cycles. Moreover, waxes do not strongly bond to the printing plate surface, i.e., they prefer to remain on the surface, rather than to actively bond to the substrate.
European Patent Application EP 0 503 621 Al discloses a direct lithographic plate making system using an ink jet system to form an ink image on the plate followed by exposure of the plate.
Considering the foregoing problems associated with the production of planographic printing plates and the limitations inherent in the prior art to overcome these problems, a series of objectives has been defined for the instant invention.
A primary objective of the instant invention is to provide a method for producing digitizable presensitized planographic printing plate intermediates from known analog type plate intermediates using ink jet printer.
Another objective of the invention is to integrate the methods of the primary objective with digital computer information systems for digital image formation and digital control of ink jet printer heads.
Another objective of the invention is to provide digitizable waterless or conventional presensitized planographic printing plate intermediates having integral masks for use with digital printing equipment.
Another objective of the invention includes a method of forming image on a presensitized waterless or conventional printing plate intermediates having a integral mask.
Another objective of the invention is to create a a printing plate by applying resinous image on a plate substrate using ink jet techniques to describe the image on the plate surface using resin forming chemicals coupled with in situ polymerization of these chemicals.